The overall objective is to determine the mechanisms of regulation of the GABA receptor/chloride (C1-) ion channel complex in rat brain. Since abnormal GABAergic neurotransmission appears to be a major factor in seizure disorders, regulation of the 'transducer' component (the GABA receptor/C1- ion channel) of GABA-ergic transmission may play an important role in the etiology and response to seizure activity. Two major biochemical tools will be used to achieve these objectives. One involves studies of the regulation of GABA receptor-gated Cl- ion channel binding sites labeled with (35S)TBPS. The other involves studies of the regulation of GABA receptor-mediated 36C1- ion flux. An important feature of these techniques is that they can be used in the same tissue from the same animals under identical conditions, something that was not possible in the past. The research plan is divided into 3 parts. The first is to determine the cellular mechanisms of regulation in vitro. Alterations in GABA receptor/C1- ion channel activity will be measured subsequent to 1) desensitizing conditions 2) alterations in membrane phospholipids by phospholipases (i.e., release of free fatty acids and subsequent formation of oxygen radicals and lipid peroxides) and 3) exposure to phosphorylating conditions. The role of these cellular processes in regulating the GABA receptor complex in vivo will be determined in the second and third parts of the research plan. In the second part, alterations in the sensitivity of the GABA receptor/C1- ion channel will be studied following repeated exposure of rats to agonists off the GABA receptor complex which are known to down-regulate GABA recognition sites. These drugs which act at 3 distinct sites on the GABA receptor complex include GABA agonists, benzodiazepines and barbiturates. Each of these drugs has anticonvulsant activity. In the third part studies are designed to measure changes in GABA receptor/C1- ion channel activity following both chemically- and electrically-induced seizures. Convulsants which act at distinct sites on the GABA receptor complex (bicuculline and picrotoxin) and maximal electroshock will be administered repeatedly over a 10 day period. The studies will provide new insights into the mechanisms that regulate GABAergic neurotransmission on a cellular level. This research should reveal the importance of these mechanisms in the actions of convulsant and anticonvulsant drugs and in the physiology of seizure activity itself.